Patent GB-653376-A (GB)
Title: Radio relay or repeater systems for the retransmission of image signals
IPC: G01S7/00
Filed: 1946-08-30
Abstract: 653,376. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 30, 1946, No. 26233. Convention date, Dec. 9, 1944. [Class 40 (iii)] [Also in Group XL (c)] A radio relay or repeater system for transmitting images of an object or the like comprises means for producing electrical image point variations representative of received signals along predetermined scanning paths in predetermined time periods, means for converting the variations produced into corresponding electrical signals during periods of time which are short relative to the firstmentioned time periods and by scanning along similar paths, a transmitter for transmitting the last-mentioned signals and means for keying the transmitter so that it is operative only for the shorter time periods whereby the transmitter is pulsed and can attain peaked power outputs in excess of its average power rating. As shown, the invention is applied to the transmission of the indication derived from a radar installation in which an antenna 11 and reflector 13 are rotated from a motor 27 which also controls a generator 39, which may be of the La Cour motor type, for the radiated pulses from the antenna 11. The received reflected pulses are applied through a receiver 41 to the control grid of a cathode-ray tube 47 whose beam 51 is given a rotational motion by coils 53 fed with sinusoidal current in quadrature from the coils of a Selsyn generator 55 driven from the motor 29. A saw-tooth voltage also is fed from a generator 61 to the Selsyn generator 55 to produce the radial motion of the beam 51. Similar control and deflecting voltages are also applied to the control grid 73 and coils 79 of a C.R. tube 71 to produce an image of the radar indication on the end 77 of the tube 71. This image is projected on the screen 87 of an iconoscope 83 scanned by a beam 89 controlled by coils 93 fed with sinusoidal current in quadrature from a Selsyn generator 95 also driven from the motor 29. Impulses from generator 39 are fed to an inverter 105 which controls a generator 99 to produce saw-tooth waves having an operative period approximately one-tenth that of the saw-tooth waves derived from the generator 61. These short period saw-tooth waves are fed to the generator 95 and control the radial scanning of the iconoscope 83. The output of the generator 95 is preferably fed through a delay network 111 so that the scanning of the projected image is deferred relative to the formation of the image on the end of the tube 71. Alternatively, the coils 93 may be displaced to produce a rotational displacement of the scanning beam. The sawtooth impulses from the generator 99 are fed through a keying unit 129 having two positions of equilibrium so that the negative bias on the control grid of the iconoscope and on the transmitter 123 is overcome during the positive portions of the saw-tooth waves applied to the generator 99 with the result that the iconoscope 83 and transmitter 123 are operative solely during the period allocated to signal transmission, shown as one-tenth of the period during which the corresponding signals are produced on the screens of the tubes 47, 71. The cathode-ray tube 71 and the iconoscope 83 may be included in a tube having a screen of which both sides are scanned and the signals corresponding to the radar indication may be applied to a storage screen which does not produce a visible image. The circuit, Fig. 3, for producing the saw-tooth waves comprises a triode 137 with a resistance 143 and condenser 147 in its output circuit, the condenser 147 being, in one case, charged when the valve is non-conducting and being discharged when the valve is made conducting by the positive impulses applied to the grid 139 to produce the long-period saw-tooth wave-form. In the other case, the valve is normally conducting so that the condenser 147 is discharged and is charged during the period of the short, negative pulses, the values of the resistance 143 and capacity 147 being modified accordingly. Specification 475,517 is referred to.